The present invention relates to gaskets for effecting watertight sealing of doors and other closures, more particularly to methods and devices for installing such gaskets in such closures.
The United States Navy's surface ship fleet includes about about eighty thousand watertight closures such as doors, hatches, and scuttles. A common feature of shipboard watertight closures is an elastic (e.g., elastomeric) sealing body known as a “gasket.” The most prevalent watertight closure gasket in the U.S. Navy's fleet is an embodiment of the “Fluidtight Door Gasket” disclosed by Marline D. Rowe and Francis A. McMullin at U.S. Pat. No. 5,553,871, issue date 10 Sep. 1996, incorporated herein by reference. The gasket disclosed by Rowe and McMullin is typically embodied as being characterized along its length by two forty-five degree chamfers and a medial semicircular groove therebetween.
The Rowe-McMullin gasket and the vast majority of other gaskets are described herein as having a “generally rectangular” cross-section. The term “generally rectangular,” as used herein to describe the cross-sectional shape of a gasket or of a gasket channel, is intended herein to convey a rectangular form that is either a perfect rectangle or a quasi-rectangle, the latter being a rectangular form that departs from perfect geometric rectangularity in certain geometric respects. Historically speaking, most watertight closure gaskets, and most watertight closure channels to which they correspond, have been characterized by a three-dimensional shape that “generally” defines a rectangular prism or a rectangular parallelepiped. “Generally” conveys that a gasket or a gasket channel may be characterized by certain design geometric deviations from a pure rectangular prismatic geometry or pure rectangular parallelepiped geometry.
The Rowe-McMullin gasket embodiment in current Navy use, illustrated in FIG. 1 and FIG. 2, is made of a Commercial Item Description A-A-59588 silicone rubber, grade 3B, class 30 composite, which is about a 30 durometer material. In terms of ease of installation, this silicone rubber material is superior to Mil-R-900 rubber (about 50 durometers), which used to be the Navy's material of choice for constituting watertight closure gaskets.
Generally speaking, the lower the durometer, the more pliable the material, and hence the easier it is for personnel to manipulate a gasket while installing it into a closure gasket channel. Nevertheless, installation of even a relatively pliable gasket requires strong hands and strong fingers to work the gasket into the entire channel perimeter; for instance, approximately seventeen linear feet of gasket is required for a typical watertight door onboard a Navy ship.
Personnel installing a gasket tend to longitudinally stretch (lengthen) the gasket, largely inadvertently, before and during insertion of the gasket into the channel. Lengthwise stretching of a gasket decreases the width of the gasket, thus making the gasket easier to install. Unfortunately, after the installation is complete, the gasket tends to relax back (shorten) to its original, pre-stretched length. This relaxation of the elastic gasket material often creates a gap between the two butt ends of the gasket, the watertight closure thereby being rendered “non-watertight.” The resultant defective gasket needs to be replaced, not due to any obvious material defect, but solely due to the gap between the two gasket ends. This gasket replacement cycle may repeat itself again and again.
The Navy's gasket is usually supplied on spools by vendors, each spool carrying a specific length (e.g., 160 feet) of the gasket. The Navy purchases enough gasket material through the stock system alone to replace every gasket on every watertight door on an annual basis. At about $3.50 per foot, this amounts to about $2,500,000 spent annually by the Navy for gasket material replacement, which is cost in addition to the time required by personnel to remove and install the gaskets.
The main reason for such high usage of the Navy's gasket is not ripping, tearing, or “permanent set” of the gasket, but rather is the elasticity of the gasket—in particular, the propensity of the gasket material to be stretched before and during installation, and to then relax back to its previous, installed length over a period of time, thereby creating a gap between the two gasket ends.